Ossa Knife is actually a trade name for Rhaphytchthys rostratus (I might have spelled the Genus name wrong). They are a very peaceful knife that can grow to 20 inches and loves to lie on its side as if it was dead. I currently house 2 Ossa knives together and they get along very well. They sleep, eat and do everything together and never bother any tankmates.
They love live worms as staple diet but take readily to frozen bloodworms, brine shrimp, mysis shrimp and even small pellets like Colorbits. They need neutral to acid water with lost of hiding places or sand to bury in. I keep mine with other knives and elephantfishes and they have been with me for about 1 year now.
Hope this helps,
Ivan